Jay Tomio at BSC Review confirms a number of speculated castings with HBO: “Joseph Mawle is Benjen Stark, Ron Donachie is Ser Rodrik Cassel, Donald Sumpter is Maester Luwin, and Ian McNeice is Ilyrio Mopatis”. All of these have been previously guessed based on GRRM’s clues, but it’s the first time that HBO has confirmed them. As the HBO source notes, these are relatively minor roles when compared to the leads, but it’s certainly good to have them made official.